A primary environmental objective, is to reduce the presence of volatile organic compounds (VOCs), chlorofluorocarbons (CFCs), perfluorocarbons (PFCs), and other toxic compounds in the atmosphere. Many of these compounds are responsible for stratospheric ozone depletion and global climatic change. Decomposition of these compounds is one of the methods available to control their emission into the atmosphere. Various techniques for decomposing compounds such as VOCs have been investigated, including: catalytic oxidation, thermal decomposition, carbon adsorption, and condensation. Unfortunately, many of these techniques are effective against only a small range of toxic compounds. Furthermore, many of these techniques are not able to decompose, cost effectively, VOCs and other toxic compounds existing in low concentrations.
Non-thermal plasma techniques, however, are capable of cost effectively decomposing various toxic compounds, particularly where the contaminant concentration is low, for example less than 1,000 parts per million (ppm). Effectives non-thermal plasma techniques include ferroelectric (high dielectric ceramics) packed-bed reactors and nano-second pulsed corona reactors. In general, these reactors produce non-thermal plasmas in which the electron mean energies are considerably higher than those of the components of the surrounding ambient gas. When electrical power is applied to these reactors, the majority of the electrical energy goes into the production of energetic electrons, rather than into producing ions and heating the ambient gas. Therefore, the plasma energy is directed to electron-impact dissociation and ionization of the ambient gas to produce radicals that, in turn, decompose toxic compounds entrained within the ambient gas. This is a more efficient and cost effective method of decomposing toxic compounds than conventional methods.
Unfortunately, the decomposition of toxic compounds using non-thermal plasma techniques produces unwanted reaction by-products such as carbon monoxide (CO), carbon dioxide (CO.sub.2), nitric oxide (NO), nitrogen dioxide (NO.sub.2), nitrous oxide (N.sub.2 O), ozone (O.sub.3), and other VOCs. Consequently, additional devices are necessary to control these undesirable by-products, thereby increasing cost and energy consumption.
It would be desirable to decompose toxic compounds and at the same time, selectively eliminate toxic by-products produced by the reaction. Furthermore, it would be desirable to perform cost effective toxic compound decomposition without elevating the temperature and reducing pressure of the gas within which the toxic compounds are entrained.